The present invention relates to electrical machines. More specifically, the invention relates to a toothless flux collector for an electrical machine.
Microturbine power generating systems include high-speed, ring-wound toothless electrical generators that are capable of delivering over 100 kilowatts of electrical power at speeds exceeding 80,000 rpm. Potential applications for microturbine power generating systems include use in off-grid applications for standalone power, on-grid applications for peak shaving, load following and base load service, emergency back-up and uninterruptible power supplies, prime mover applications (e.g., pump, air conditioning) and automotive hybrid vehicles.
Toothless flux collectors are used in the high-speed, ring-wound toothless electrical generators. A toothless flux collector is disclosed by Joseph Denk in U.S. Pat. No. 4,852,245, which is assigned to the assignee of the present invention. Unlike conventional flux collectors, the toothless flux collector does not have T-shaped teeth extending radially inward. The teeth are known to cause problems such as cogging, higher magnetic spring rate and rotor heating due to eddy currents induced by slot ripple. Additionally, the teeth add to the cost and complexity of fabricating the flux collector. Eliminating the teeth either eliminates or reduces these problems.
A toothless flux conductor for an electrical generator of a microturbine power generating system can be fabricated from iron powder particles that are individually coated with an electrical insulating material and sintered into a core. In the alternative, the flux conductor can be fabricated from thin plate-like laminations that are stacked together into a core. Prior to stacking, faces of the laminations are coated with an electrical insulating material.
Lamination stacks tend to have higher end losses than powder metal cores. However, powder metal cores tend to have lower permeability and lower saturation. Moreover, both the powder metal cores and lamination stacks are relatively expensive to fabricate. They are both fabricated using relatively complicated tooling and they both have long lead times.
There is a need for a toothless flux collector having lower iron losses than the lamination stacks and higher permeability and saturation than the powder metal cores. There is also a need for a toothless flux collector that can be manufactured at a lower cost than the lamination stacks and powder metal cores.